This is a new R21 application to characterize co-infection of mice with murine gammaherpesvirus 68 (MHV68)androdent Plasmodiumspecies. Atightassociation between EBV infection and Plasmodiumfalciparum malaria in young children is known in the genesis of endemic Burkitt's lymphoma (eBL) - although this only occurs in a small minority of co-infected individuals. In many regions of central Africa, Plasmodium falciparum malaria is the leading cause of death of children under 5 years old [e.g., in the Central African Republic it is estimated to account for 34 deaths per 1,000 children < 5 yrs of age]. Factors contributing to the variable outcome of P. falciparum infection in young children remain largely undefined. Importantly, it is not known whether there are other pathologic manifestations of EBV and P. falciparum co-infections (e.g., does EBV co-infection in some children contribute to morbidity and mortality from P. falciparum). While a number of studies have identified alterations in the host response to EBV infection in children with malaria, the actual contribution of co-infection (particularly, the timing of acute EBV and P. falciparum infections) has not been rigorously addressed due to limitations in obtaining appropriate prospective patient samples, as well as the inability to control parameters of infection. There are several rodent Plasmodium species that have been routinely used in mice to model aspects of Plasmodium infections in humans. We have initiated studies on co-infection of mice with a murine gammaherpesvirus, MHV68, and P. yoelii to assess how co-infection may alter the outcome of chronic MHV68 infection - as well as its impact on P. yoelii infection. Our preliminary data [as well as the studies of Haque et al.] have demonstrated a strong synergy between co-infection of mice with MHV68 and P. yoelii - providing an experimental model in which interference in normal host control of both Plasmodium and gammaherpesvirus infections is observed. To extend these studies we propose the following 2 specific aims: Aim 1. Characterize enhanced pathology in mice co-infected with rodent Plasmodium species and MHV68: Aim 1.1. Determine timing of MHV68 and P. yoelii or P. chabaudi co-infection vs. severity of disease; Aim 1.2. Characterize pathological changes in co-infected vs. singly infected animals; Aim 1.3. Monitor progression of malaria and virus infections in singly and co-infected mice; and Aim 1.4. Characterize cytokine, T cell and B cell responses in singly and co-infected mice. Aim 2. Identification and characterization of specific factors contributing to lethality of Plasmodium infections in MHV68 infected mice: Aim 2.1. Identify viral genes contributing to disease severity; Aim 2.2. Determine impact of anemia-associated hypoxia on virus reactivation/persistent replication; Aim 2.3. Examine impact of anti-malarial and anti-viral treatment on disease severity; and Aim 2.4. Assess long-term sequelae from co-infection under conditions that favor animal survival.